1. Field of the Invention
The present invention relates to a thin film transistor and a method of fabricating the same, and more particularly, to a thin film transistor having a polysilicon semiconductor layer, and a method of fabricating the same.
2. Description of the Related Technology
Conventionally, a polysilicon layer has been widely used as a semiconductor layer for a thin film transistor, since it has high electric field effect mobility to be adapted to a high-speed circuit and a complementary metal oxide semiconductor (CMOS) circuit. A thin film transistor having such a polysilicon layer is used in an active device of an active matrix liquid crystal display (AMLCD), and a switching device and a driving device of an organic light emitting display (OLED).
The polysilicon layer used in the thin film transistor may be manufactured by a direct deposition method, a high temperature annealing method, or a laser annealing method. The laser annealing method can be performed at a low temperature and may implement high electric field effect mobility. However, since the laser annealing method requires a very expensive laser equipment, alternatives have been actively sought.
Currently, a method of crystallizing amorphous silicon using a metal is being widely researched since it can crystallize amorphous silicon at a lower temperature, compared to solid phase crystallization. The crystallization method using a metal may includes a metal induced crystallization (MIC) method and a metal induced lateral crystallization (MILC) method. However, in the case of the method of using a metal catalyst, characteristics of the thin film transistor may be degraded due to contamination caused by the metal catalyst.
In order to prevent the contamination caused by the metal catalyst, a crystallization method of fabricating a polysilicon layer using a capping layer is disclosed in Korean Patent Application Publication No. 2003-60403. The method includes depositing an amorphous silicon layer and a capping layer on a substrate, forming a metal catalyst layer on the substrate, diffusing the metal catalyst into the amorphous silicon layer through the capping layer using an annealing method or a laser annealing method to form a seed, and forming a polysilicon layer using the seed.